Evolution Not Over for Humans

"It's a subtle signal, but we find genetic evidence that natural selection is happening in modern human populations," said study co-author Joseph Pickrell, an evolutionary geneticist at Columbia University and the New York Genome Center.

Pickrell and his colleagues explored the genomes of 60,000 people of European descent from California and 150,000 from Great Britain. The researchers looked for signs of mutations that are linked to longer life spans.

The researchers found that a genetic variation linked to Alzheimer's appears to fading in older women, possibly because women who have it tend to die earlier. They also found similar evidence that a genetic variation linked to heavy smoking in men is becoming less common.

"It may be that men who don't carry these harmful mutations can have more children, or that men and women who live longer can help with their grandchildren, improving their chance of survival," said co-author Molly Przeworski in a Columbia news release. She is an evolutionary biologist at the university.

There's also evidence that genetic variations linked to heart disease, high cholesterol, obesity and asthma may be on the decline, the researchers added.

"The environment is constantly changing," said study co-author Hakhamenesh Mostafavi, a Columbia graduate student. "A trait associated with a longer life span in one population today may no longer be helpful several generations from now, or even in other modern-day populations."